1. Technical Field
The present invention generally relates to a method and apparatus for removing contaminants from a workpiece, such as a semiconductor. In particular, the present invention relates to an apparatus and method for removing contaminants from a workpiece using chemically reactive additive to promote the effectiveness of surface tension gradient drying.
2. Description of Relevant Art
A variety of methods have been attempted to achieve drying of wafers. One common method utilizes a centrifugal dryer, which unfortunately places mechanical stresses that may result in breakage of the wafer. Also, since it is difficult to avoid evaporation of water on the wafer surface during spinning by the centrifugal dryer, dissolved silicates or suspended solids may precipitate onto the surface of the workpiece, leading to device failure.
Chemical vapor drying or chemical solvent drying have the disadvantages that the chemical often forces dissolved or suspended solids such as silicates or colloidal silica to precipitate onto the surface of the workpiece, leading to device failure. A second disadvantage is that chemical vapors and solvents do not completely remove moisture and chemical/particulate impurities or contaminants. A third disadvantage is that chemical vapors and solvents have not been chosen to control acidity and basicity to dissolve minerals such as silicate to avoid precipitation on the workpiece during drying. A fourth disadvantage is that chemical vapors and solvents do not create a buffer to maintain a constant pH to effect particle removal by taking advantage of the relationship between particle zeta potential and pH. Thus a need exists to more adequately remove contaminants from a workpiece and improve drying methods for various workpieces.
Matthews, 1999, in U.S. Pat. No. 5,911,837, Mohindra et al., 1996, in U.S. Pat. No. 5,571,337, McConnell et al., 1991, in U.S. Pat. No. 4,984,597, Leenaars et al., 1993, U.S. Pat. No. 5,271,774 and Leenaars, 1990, European Patent No. 0 385 536 A1 disclose examples of drying apparatuses.
According to one aspect of the present invention, a method for removing contaminants from a workpiece is provided. The method includes the following steps: (1) providing a workpiece; (2) contacting the workpiece with a liquid; and (3) removing the liquid from said workpiece using a chemically reactive additive.
According to a second aspect of the present invention, a method for removing contaminants from a workpiece is provided. The method includes the following steps: (1) providing a workpiece; (2) contacting the workpiece with a liquid; (3) withdrawing said workpiece from said liquid, such that a portion is submerged in the liquid, and a remaining portion is exposed to a chemically reactive additive; (4) developing a concentration gradient of said chemically reactive additive in said liquid film; and (5) removing the liquid film from said workpiece using said concentration gradient of said chemically reactive additive in said liquid film.
According to a third aspect of the present invention, a method for removing contaminants from a workpiece is provided. The method includes the following steps: (1) providing a liquid bath; (2) providing a workpiece submerged in said liquid bath; (3) providing a chemically reactive additive diffusion limiting barrier over said liquid bath and a chemically reactive additive over said chemically reactive additive diffusion limiting barrier; (4) extending a portion of the workpiece over said surface of the chemically reactive additive diffusion limiting barrier, wherein said portion is covered with a liquid film and wherein said portion of said liquid film includes some of said chemically reactive additive; (5) developing a concentration gradient of said chemically reactive additive in said liquid film; and (6) removing the liquid film from said workpiece using said concentration gradient of said chemically reactive additive in said liquid film.
According to a fourth aspect of the present invention, an apparatus for drying a workpiece is provided. The apparatus includes: (1) a liquid bath; (2) a workpiece, wherein a part of the workpiece is submerged in the liquid bath, and wherein a remaining part extends above the liquid bath and is surrounded by a chemically reactive additive; and (3) a liquid film on the part of the workpiece extending above the liquid bath, wherein the liquid film has a concentration gradient of the chemically reactive additive.
According to a fifth aspect of the present invention, an apparatus for drying a workpiece is provided. The apparatus includes: (1) a liquid source; (2) a rotating workpiece; and (3) a liquid film on the surface of the rotating workpiece, wherein the liquid film is exposed to a chemically reactive additive and wherein the liquid film has a concentration gradient of the chemically reactive additive.
Workpieces, such as silicon wafers, often undergo a series of wet chemical steps during processing. If removal of the residues from these chemicals is incomplete or if soluble silicates or insoluble silica that are byproducts from reaction of the chemicals with the wafer remain on the surface of the wafer, device failure may result. It is therefore an advantage of the present invention to provide an apparatus and method to remove these contaminants from a workpiece, such as a silicon wafer, without leaving contaminants on the surface of the workpiece that may result in device failure. A second advantage of the present invention is to provide an apparatus and method to remove typical contaminants such as soluble and insoluble metal oxides and hydroxides, mineral particulates, colloidal silica and silicates from a workpiece, such as a semiconductor wafer, by chemically dissolving them by exposing the workpiece to the chemically reactive additive. A third advantage of the present invention is to provide an apparatus and method to control the equilibrium between contaminants such as soluble silicates (SiO3xe2x88x922) and insoluble silica (SiO2). A fourth advantage of the present invention is an apparatus and method to remove contaminants by exposing the workpiece to the chemically reactive additive without pitting the workpiece by controlling the temperature and pH of the liquid film, the concentration of the chemically reactive additive over the liquid bath and the rate at which the wafer is exposed to the chemically reactive additive. A fifth advantage is an apparatus and method to use a mixture of acidic and basic chemically reactive additives (e.g. NH3 and HCl) to create a buffer to maintain a constant pH to effect removal of contaminants by taking advantage of the relationship between contaminant particle zeta potential and pH.